t looks like the bastardized version of a gymnast's somersault, the parkour roll, but it's the most difficult parkour technique to master. In its own deceptive way, it's also the most dangerous.

Start with the stance, a squatting position with the knee of your dominant foot pointed forward, the other knee at a perpendicular angle to the side. With back straight, turn your torso slightly away from your dominant knee, cock your head toward your other knee, and push your arms straight in front of you with elbows locked and palms facing outward. Make the tips of your middle fingers kiss. Fall forward. Your body should roll from the back of the shoulder on your dominant hand's side to the opposite hip, cradling your spine and protecting your head.

Executed properly, the roll assists parkour practitioners as they maneuver the concrete jungle of Baltimore, leaping over guard rails and bike racks, running through parking garages, and jumping down from heights of 10 feet or more. The preferred term for these running rogues is traceurs, French because of parkour's origins. In France parkour was used to train firefighters to maneuver around obstacles; it was also a military discipline. Americans might know parkour from the opening chase scene of the 2006 film "Casino Royale": a lanky man fleeing a muscled Daniel Craig glides his body through a narrow opening, whereas Craig punches himself through the drywall. The exact evolutionary history is murky, but credit to taking parkour to the streets for the first time, in the late 1980s, goes to Frenchman David Belle.

In parkour, as Belle demonstrated, you don't go around a fence; you jump over it.

And instead of coming to a dead stop after each vault or jump, you roll to salvage some of your kinetic forces and transfer them to the next vault or jump, while cushioning the blow of excessively high leaps. A somersault is no good, as a traceur will end up with bruises down the length of their spine. But a roll done improperly could leave a person with a dislocated shoulder, a bruised hip, a lacerated forearm, or a concussion from slamming the back of their head onto concrete.

Despite Adam McConnell's instruction, I'm struggling to get it right. McConnell is the 32-year-old owner of the new 15,000-square-foot Urban Evolution gym on Eastern Avenue, past the Johns Hopkins University Bayview Campus. For six years he has been a traceur, and now he's teaching locals the skills and techniques of parkour in the hopes they, too, will try taming asphalt.

During an introductory class in late August, I have the fortune of attempting this parkour roll on a padded mat. But I'm no good — I'm rolling sideways on my hip, and not diagonally across my back-and McConnell singles me out in this class of five, and makes me try several backwards rolls to see if I can feel the difference.

By the end of this two-hour class, I'll have jumped into squatting position on elevated pieces of two-by-four, rolled incorrectly about a dozen times, and speed-vaulted over trapezoidal wooden boxes over three feet high, marveling in mid-air that my left hand is powerful enough to help me clear a box more than half my height without my feet needing to touch the top of it.

For a 24-year-old I consider myself spry. Not overly athletic, but in good health: A physician in June told me I have perfect blood pressure. But after this class, I'm out of breath. My quads ache, and it's difficult to walk down steps without a rail to lean on.

"Welcome to real parkour," McConnell says, a coy reference to a tale I told of inebriated college friends jumping off benches, clicking their heels, and shouting "parkour!"

In the United States, parkour is slowly but forcefully gaining steam as a new, quasi-sport. Traceurs in Baltimore's nascent parkour community train in and around the Inner Harbor amphitheater, in front of the Maryland Science Center, and inside nearby parking garages. It's a growing scene, bolstered by college undergraduates and loosely organized by local traceurs who communicate via text and the B-more Awesome Facebook Group. At Otakon in August, a parkour jam took place, as it has the previous several Otakons, with traceurs showing off new tricks. They soar into the air by kicking off walls, hanging like cats off other walls, and flipping off of concrete barriers.

McConnell counts himself in the second generation of traceurs in the U.S., but one of its first "gym rats." His month-old gym is the fourth Urban Evolution to open, and the largest parkour gym on the East Coast, he says. It's a sprawling warehouse, the former home of a mayonnaise-production facility, filled with mobile, wooden obstacles, makeshift monkey bars, and a 750-pound tire. Graffiti covers the walls.

But gym-based parkour isn't real parkour (it's "parkour training"), because real parkour is done in the real world with real consequences. In his left leg, McConnell sports a tiny divot, the remnant of slamming his shin into a metal bar. A bruise formed, and then a scab, and then one day McConnell tore it off inadvertently when he pulled his pants on. A quarter-sized crater was left, into which McConnell inserted a pencil and started tapping. "It was my bone," he says.

Can Gün Yaprak, a 22-year-old mechanical engineering major at the University of Maryland, Baltimore County, started doing parkour in 2010. He works at the Baltimore gym — although McConnell has no money yet to pay employees — but can't do any teaching thanks to a massive brace on his right knee that's not coming off for another six months. Yaprak one night tried a front flip outside. His knees locked up, and when he landed, his right kneecap popped backward, leaving him looking like an ostrich and rupturing a ligament, before it popped back into place.

"A lot of parkour is just having the balls to try something," Yaprak says. Balls, indeed.

Take Stephen Callender, a 22-year-old from Pikesville who knows McConnell from having trained with him in the Inner Harbor. Like Yaprak, Callender has his own story of a flip gone wrong. A misjudged sideflip gave him a dislocated shoulder — "It wasn't that bad," he says — which he popped back in with the help of another traceur.

Though McConnell and others insist parkour is more than a means of front-flip-induced physical masochism. On some days you'll find Omar Tamimi, 21, training around the Inner Harbor where it meets the Maryland Science Center, using the exercise of parkour to keep the inflammation from a medical condition in check. Tamimi, a fifth-year physics major at the University of Maryland Baltimore County, is another of McConnell's instructors.

Still, cries of pain routinely abound. I attempted what's called a kong vault over a wooden obstacle during my intro class, and had my body horizontal in air in relation to the top of the obstacle-as it's supposed to be-just before slamming my face into a floor mat.

"There's always the understanding that the training of parkour is very difficult," says Callender. "But I'll go back to spaces I've walked through my entire life, and now I look at them totally differently."

This attitude about one's relationship to physical space, and how much a person is limited by their movements, is perhaps the biggest argument put forward by traceurs about parkour's reason for being.

"We are challenging the concept of what is public space," says McConnell. "I want this to be something people do in their everyday life."

It's a lofty, maybe even farfetched, idea. Can you imagine shaving seconds off your work commute with a well-placed vault over a park bench? Or being harassed by security guards in parking garages and parents on playgrounds, as McConnell has been, for engaging in an activity that could concuss the doer?

"If we hit a handrail and it breaks, it needed to be replaced anyway. We're doing a public service," McConnell says. And what about, he asks, kids who are obese? Or "bored" adults, people who have forgotten the childlike joy of simply having fun?

It's an easy argument to ridicule, but McConnell is a man driven by conviction. Parkour, quite literally, changed his life. He was working in agricultural consulting until he saw parkour's originator, Frenchman David Belle, leaping, vaulting, and flipping over thugs in the Paris ghettos depicted in the 2004 film "District B13." He soon found himself at a weekend training session at the Silver Spring Metro station, where he tried to endure three rounds of parkour conditioning drills, such as pinning himself horizontally between two close walls and using hands and feet to travel 35 feet. McConnell lasted one round, but he returned the following weekend,

"I'm trying to save this discipline from something people just do in the gym," he says.

To do so in Baltimore, though, he'll need his gym to train the unenlightened masses. Remember: Stretch your quad muscles beforehand.

TRY IT YOURSELF

Urban Evolution is at 6801 Eastern Ave. and offers mutiple kinds of classes throughout the week, for all ages. For a class schedule and more information, go to urbanevo.com.

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